1. Field of the Invention
The present invention relates to a field emission device, and more particularly to a field emission device having a grid electrode.
2. Background
Field emission devices are based on emission of electrons in a vacuum, and emit light by electrons emitted from micron-sized tips in a strong electric field, accelerating, and colliding with a fluorescent material. The field emission devices are thin and light with high brightness.
Diode field emission devices having a conventional structure can be easily manufactured. However, they are disadvantageous in controlling emission current and realizing a moving picture or gray-scale picture. Accordingly, instead of a diode structure, a triode structure is commonly required.
Referring to FIG. 4, a typical triode field emission device includes a cathode electrode 40, an anode electrode 45, and a grid electrode 43 located therebetween. A vacuum chamber between the cathode electrode 40 and the anode electrode 45 is maintained by several spacers 44. The cathode electrode 40 has a number of fine emitters 41 formed thereon. Generally, an insulating layer 42 is arranged between the cathode electrode 40 and the grid electrode 43, electrically isolating the cathode electrode 40 and the grid electrode 43. The insulating layer 42 includes a number of tiny through holes corresponding to the emitters 41. The grid electrode 43 is arranged on a top surface of the insulating layer 42, for extracting electrons from the emitters 41.
Nevertheless, during the electron emitting process, it is unavoidable that some of the emitting electrons are captured by the grid electrode 43. In particular, when the grid electrode 43 is provided with a high voltage, the attraction between the grid electrode 43 and the emitting electrons is stronger, and the number of captured electrons increases. As a result, an emitting efficiency of the whole device is reduced, and the energy efficiency of the field emission device is also reduced.